Various information processing systems have been developed to meet the demands of the rapid expansion which has taken place in the information industry in recent years, and methods of recording and apparatus compatible with these information processing systems have been developed and adopted. Heat sensitive recording methods are such that the apparatus used is light and compact, there is little noise associated with the apparatus and they have excellent operability and maintenance characteristics and, since they also allow coloring to be achieved easily, these methods are the most widely used.
The heat sensitive transfer recording systems can be broadly classified into two types. In the first type, heat is imagewise applied from the support side to a thermofusible ink which has been coated onto the support and the ink is fused in the form of the pattern in which the heat has been applied and transferred to the recording medium to provide a hard copy. In the second system, heat is applied from the support side in the same way as before to a heat sensitive transfer sheet which has, on a support, a layer which contains a dye which is sublimed or rendered mobile by heat, the dye migrates into the recording medium (receiving sheet) in the form of the pattern in which the heat has been applied and a hard copy is obtained.
The recording media (thermal transfer receiving sheets) used here have a receiving layer comprising a resin which is easily dyed with dyes which receiving layer is coated on, or attached by pressure to, a base sheet such as paper or a PET base.
Among the properties required of the base sheet, it should be capable of forming an image of high density as a result of the transfer and it should provide good image storage properties with no fading of the image even on ageing after the image has been formed.
The composition of the receiving layer can be improved and the diffusibility of the dye can be increased with a view to raising the transfer density.
Furthermore, image fading arises as a result of movement in the receiving layer itself and diffusion of the dye, and if the base sheet has properties which enable the dye to diffuse, it is diffused through the base sheet and image fading occurs. It is clear that fading of the image occurs for this reason especially when polyethylene coated papers are used for the base sheet. Consequently, there is a problem in that fading of the image is liable to occur when resins which provide high dye diffusibility are used with the intention of increasing the transfer density on a polyethylene coated paper.